FAmilial influences have been demonstrated on individual sex-steroid hormones. These influences are partly genetic and partly due to concomitant environmental factors such as nutritional intake, age, obesity, smoking, and alcohol consumption. There are also phenotypic associations among sex-steroid hormones and among hormones and related epidemiological measures. Whereas the genetics of individual hormones have been characterized fairly well, research to date has not examined the nature of the genetics of covariation among hormones, and there are many gaps in our understanding of the familial and nonfamilial factors underlying the interrelationships among hormones and related lifestyle and environmental variables. The proposed research will analyze previously collected twin data on sex-steroid hormone levels and related variables in adult Caucasian male twins. Specifically, it will test whether phenotypic covariation among hormones within individuals is a consequence of genotypic influences common to multiple hormones, environmental influences that are shared by family members, or environmental influences that are unique to each individual. This will be accomplished using existing methods of multivariate analysis of covariation in twins. Similarly, the source of the covariation among hormones and related lifestyle and environmental factors will be characterized. New methods of analysis of multivariate twin data will be developed and implemented to accomplish this goal. The characterization of these interrelationships will provide data for developing research hypotheses regarding the metabolism of hormones and will provide focus for clinical intervention strategies for modifying abnormal hormonal levels. The new methods that will be developed will be widely applicable to other studies which employ the classical twin design using multivariate data.